1. Field of the Invention
The present invention relates to heat exchangers and, more particularly, to recuperators for use with turbines and turbo-alternators.
2. Description of the Prior Art
Many gas turbine engines use a heat exchanger or recuperator to increase the operational efficiency of the engine by extracting heat from the exhaust gas of the engine and preheating the intake air before it is passed to a combustor section of the engine. Typically, a recuperator for a gas turbine engine is annular-shaped in cross section and positioned around the engine. Such xe2x80x9cannularxe2x80x9d recuperators generally include a core which is commonly constructed of a plurality of relatively thin, flat metal sheets having an angled or corrugated spacer fixedly attached therebetween. The sheets are joined into cells and sealed at opposite sides, forming passages between the sheets. The cells are stacked or rolled and form alternating cold air intake cells and hot air exhaust cells. The hot exhaust air from the engine heats the sheets and the spacers; and the cold air cells are heated by conduction from the sheets and the spacers.
One annular heat exchanger is known from U.S. Pat. No. 5,081,834 to Darragh. The heat exchanger disclosed by the Darragh patent is configured to resist the internal forces and pressures and the thermal stresses inherent from the cyclic operation of a gas turbine engine. The core of the heat exchanger disclosed by the Darragh patent has a plurality of heat recipient passages which have a uniform cross-sectional area throughout the entire length of the passages. In addition, the core has a plurality of heat donor passages which have a uniform cross-sectional area throughout the length of the passages. The heat recipient passages contain a heat recipient fluid during operation and the heat donor passages contain a heat donor fluid during operation. The core includes a plurality of stacked primary cells each defining one of the passages (heat recipient passages or heat donor passages) therein. The cells are secured together forming a generally annular shaped core in cross section. Each of the plurality of cells has an involute curve shape and includes at least a pair of primary surface pleated sheets.
A major disadvantage with heat exchangers such as that disclosed by the Darragh patent is that the heat recipient passages and the heat donor passages are defined by a plurality of metal sheets that extend between an inner diameter of the heat exchanger and an outer diameter of the heat exchanger. Each of these sheets is a potential leak path between the heat donor fluid and the heat recipient fluid, which will degrade the efficiency of the heat exchanger and the power output of the engine.
Accordingly, an object of the present invention is to provide a recuperator for use with a turbine or a turbo-alternator that reduces the possibility of leakage between a heat donor fluid and a heat recipient fluid. It is a further object of the present invention to provide a relatively inexpensive recuperation for use with a turbine or a turbo-alternator.
The above objects are accomplished with a cylindrical or annular shaped recuperator made in accordance with the present invention.
The present invention is a fluid recuperator that includes a frame, an enclosure provided about the frame defining a recuperator chamber, a first fluid inlet in fluid communication with the recuperator chamber, a first fluid outlet in fluid communication with the recuperator chamber, a plurality of spaced sealed recuperator units received within the recuperator chamber, each of the recuperating units having a body with an outer surface and an inner surface that defines a second fluid flow chamber, a second fluid inlet in fluid communication with the plurality of sealed recuperator units and a second fluid outlet in fluid communication with said plurality of sealed recuperator units. The recuperator is adapted to have a first fluid flow through the first gas inlet, the recuperator chamber across the sealed recuperator units outer surface and through the first fluid outlet, respectively, while a second fluid passes through the second fluid inlet, through the second fluid flow chambers, contacting inner surfaces of the sealed recuperator units and through said second fluid outlet in a manner that the first fluid and the second fluid do not mix while passing through the recuperator chamber and heat transfer takes place between the fluids through the bodies of the sealed recuperator units.
The present invention is also a method for manufacturing a sealed recuperator unit, that includes the steps of:
(a) providing a first section having an embossment;
(b) providing a second section;
(c) placing a corrugated member in the embossment;
(d) placing the second section over the first section; and
(e) welding said first section to said second section thereby forming a sealed recuperator unit.
The present invention is also a method for cleaning the above described recuperator, that includes the steps of:
(a) removing at least one of said open recuperator units which is fouled; and
(b) replacing the removed open recuperator unit with a cleaned recuperator unit.
The present invention is also a method for forming a joint, that includes the steps of:
(a) providing a first metallic member having a first thickness and having a lip;
(b) providing a second metallic member having a slot for receipt of the lip, the second metallic member having a second thickness, the second thickness is greater than the first thickness;
(c) placing the lip within the slot so that a tip of the lip extends beyond the slot;
(d) heating the tip until the tip melts;
(e) heating the second metallic member adjacent the tip so that the melted tip causes the first metallic member to weld to the second metallic member about the lip; and
(f) permitting the first metallic member and the second metallic member to cool, thereby forming a welded joint about the lip.
Further details and advantages of the present invention will become apparent with reference to the following detailed description, in conjunction with the drawings.